Many integrated circuits (“ICs”) need circuitry, such as an initial controlled current source for biasing or use as a reference, which starts up before the rest of the IC. This “start-up” circuitry controls and facilitates the start up of other portions of the IC.
It is easier to facilitate the biasing of the IC if there is some amount of control over the accuracy and the performance of the start-up circuit. It is also advantageous to have a current source that starts when the supply voltage is as low as possible and does not fail when the supply voltage “spikes” to a high level. For example, in the automotive industry, although a car has a 12 volt battery, the voltage can go as high as 40 volts to as low as 3 volts during some transient conditions.
Some current start-up circuitry does not operate at a wide enough supply voltage range to meet the needs of some applications, such as the above automotive example. Other start-up circuitry is complex due to the numerous components contained in the circuitry. This complex start-up circuitry can occupy too much area on the IC and consume more current than desired.
Embodiments presented herein are illustrated by way of example, and are not limited by the accompanying figures, in which like references indicate similar elements. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present disclosure.
The methods and circuitry components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.